Method of treating oriented acrylonitrile structures



y 3, 1948. s. SILVERMAN 2,445,042

IBTHOD 0P TREATING ORIENTED ACRYLONITRILE STRUCTURES Filed July 28, 1943.Wai

IN V EN TOR. SH/R4 5/6 5/4 VERMN h/im/ A TTOR/VEX Patented July 13, 1948IV IETHOD OE TREATING ORIENTED ACRY- LONITRILE STRUCTURES ShirleighSilvcrman, Baltimore, Md., assignor to E. I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware Application July28, 1943, Serial No. 496,396

Claims. 1

This invention relates to shaped articles, such as yarns, films,tubings, fibers, etc., of an acrylonitrile polymer. More particularly,it relates to a method for improving the physical properties of suchshaped articles which have been subjected to a drawing operation duringor after their formation and which show a definite orientation on X-rayanalysis.

For convenience, this invention will be discussed in connection with thetreatment of yarns of an acrylonitrile polymer.

It has been proposed to dissolve an acrylonitrile polymer in a suitableorganic solvent and extrude the resulting solution through an orifice toform a shaped structure, such as a yarn. When little or no tension isexerted on the yarn during the spinning operation, the yarn obtained issomewhat brittle and possesses undesirably low properties. A typicalyarn will possess a tenacity of approximately 0.8 gram per denier and anelongation of about 8%. X-ray analysis indicates that the yarn iscrystalline in nature but substantially unoriented.

There have recently been proposed two methods involving the. stretchingof an acrylonitrile polymer yarn, whereby it is possible to greatlyincrease the tenacity of such a yarn without causing any substantialdecrease in its elongation. According to one of these methods, which isfully described in copending application of Daniel T. Meloon, Serial No.496,397, filed July 28, 1943, the substantially unoriented yarnmentioned above is heated to a temperature of at least 100 C. and drawnwhile at this temperature to from 4 to 10 times its original length.According to the second method. which is fully disclosed in copendingapplication of William W. Watkins, Serial No. 496,376, filed July 28,1943, now Patent No. 2,426,719, the yarn is spun by a wet-spinningtechnique into a bath comprising, for example, a glycerol bath heated toa temperature of 140 C. or an aqueous 40% calcium chloride bath heatedto a temperature of at least 100 0., the yarn being subjected during itspassage through the bath to a tension of at least 0.5, and preferably0.7 to 1.0 gram per denier.

The yarns obtained by either of these two methods are highly orientedand generally possess a tenacity of at least 3 grams per denier.However, they still possess an elongation that is relatively low, itbeing of the order of 8% to 12%. While they can be used for certainspecialized purposes, wherein a low elongation is desirable,

- the yarns are not generally suited for use in the textile art, whichrequires a yarn possessing an elongation of from 15% to 25%, andpreferably of from 18% to 22%.

It is the object of this invention to provide an acrylonitrile polymeryarn suitable for use in the textile art. It is a further object of thisinvention to provide a method for improving the elongation of anoriented acrylonitrile polymer yarn. It is a still further object of theinvention to provide a method for improving both the tenacity andelongation of an oriented acrylonitrile polymer yarn. Itis a specificobject of the invention to provide an acrylonitrile polymer yarnpossessing a tenacity of at least 3 grams per denier and an elongationof at least 15%. Other objects will become apparent hereinafter,

The objects of this invention are accomplished, in general, by heatingan oriented acrylonitrile polymer yarn in a relaxed state to atemperature of at least 6., whereby the yarn is caused to shrink, andthen maintaining the yarn at a temperature of at least 80 C. for aperiod of from 1 to 24 hours, the yarn during this time being maintainedin a relaxed state or under very low tension, for example, a tension ofapproximately 0.05 gram per denier. The term oriented acrylonitrilepolymer yarn, as used in this specification, refers to an acrylonitrilepolymer yarn that possesses a tenacity of at least 3 grams per denierand an elongation of from 8% to 12% and that showspn X-ray analysis adegree of orientation at least equal to that of an acrylonitrile polymeryarnspun by the dry-spinning technique without the application ofstretching tension, as disclosed in Example I of copending applicationof George H. Latham, Serial No. 447,466, now abandoned, subsequentlystretched to at least twice its original length while passing through aglycerol bath maintained at a temperature of C., as disclosed in saidcopending application of Daniel T. Meloon, Serial No. 496,397, filedJuly 28, 1943.

The initial step of this process; involving the hot relaxing of theyarn, causes it to shrink 10% to 25% of its length, this shrinkage ofthe yarn not affecting its tenacity but causing a large increase in itselongation, substantially all of this shrinkage showing up as increasedelongation. This latter result is surprising and is in sharp contrast tothe action of other stretched polymeric yarns, wherein only a portion ofthe total shrinkage of the yarn at elevated temperatures shows up inincreased elongation. At the same time, this hot relaxing of the yarncauses an appreciable improvement in its other properties, including anapproximate 50% increase in such properties as knot, loop and impactstrength.

The final step of the process involving a prolonged heating of theshrunken yarn, preferably accomplished under no or only very slighttension, does not generally cause a further shrinkage of the yarn butrather causes an appreciable and surprising increase in its tenacitywithout any accompanying substantial loss in its elongation. The yarnthus ebtained is in condition for subsequent use, for example, in thetextile art.

In contrast to the untreated yarn, it possesses a somewhat increasedtenacity, a greatly improved elongation and a desirable increase in itsother physical properties, including such properties as knot, loop andimpact strength, etc. Moreover, the final yarn does not appear to'havebeen degraded by the successive heat treatments involved in the processof this invention.

The practice of this invention is not limited to the use of a particulartype of apparatus and, generally speaking, any form of apparatus capableof heating the yarn in the desired manner can be used.

In the drawings,

Figure 1 shows a diagrammatic form of one embodiment 01' an apparatussuitable for use in the invention; and

Figure 2 is a perspective view of one form oi. heating device which issuitable for use in the invention.

Referring now to Figure 1, an oriented acrylonitrile polymer yarn I isunwound at a constant rate from a supply bobbin 2 by a metering devicecomprising a positively driven roller 3 and displacement guide I, and isled through a heating means 5 by a second metering device comprising apositively driven roller 6 and displacement guide I. The speed of thepositively driven roller 6 is so adjusted with respect to that of thepositively driven roller 3 that the yarn I, passing through the heatingmeans 5, is in a relaxed state and free to shrink. The shrunken yarnleaving the second metering device is then collected in package form ona rotating bobbin 8, the yarn being preferably wound into the packageunder the lowest possible tension commensurate with good winding andunwinding performance. The wound package is then placed in an oven whereit is maintained at a temperature of at least 80 C. for a period of 1 ormore hours.

The heating means 5 must, of course, be so constructed that it iscapable of heating the yarn passing through it to the desiredtemperature without exerting any tension on it, the yarn being free toshrink at all times during its passage through the device.

Referring now to Figure 2, wherein there is shown one form of apparatuscapableiof operating in such a manner, the reference numeral 20designates a solid block provided along one 'surface with a. slot 2|throughwhich the yarn I is led." The block 20 is provided with a bore 22in which there is positioned an electrical resistant 23 capable ofmaintaining the block at the desired temperature of at least 80 C. Theblock 20 is preferably made of metal whereby the yarn I, passing throughthe slot 2 I, will be heated both by convection and radiation. As shown,the slot II is preferably enlarged at that portion thereof through whichthe yarn passes.

The following examples which are intended to illustrate, and notrestrict, the invention represent several preferred embodiments of theinvention,

and the percentages therein given are by weight:

Exam: I

An acrylonitrile polymer yarn was prepared by the extrusion oi. a 25%solution of an acrylonitrile polymer having a molecular weight of 66,000in tetramethylene cyclic sultone through a, Ill-hole spinneret into atubular cell through which heated air was circulated in an oppositedirection. The yarn issuing from the cell had a denier of 310 andpossessed a tenacity of 0.8 gram per denier and an elongation 01' 8.0%.X- ray analysis showed it to be crystalline in nature butsubstantlallyunorlented. The yarn was then stretched between positivelydriven rollers and, while passing about a stationary pin, heated to atemperature of C. to 8 times its original length. The stretched yarnpossessed a tenacity 01 3.7 grams per denier and an elongation of 10.1%.x-ray analysis showed it to be crystalline in nature and highly orientedin the direction of its fiber axis. 1 7

The yarn was then passed in the continuous, relaxed manner of Figure 1oi! the accompanying drawings through a slot formed in a metal block 10inches long and maintained at a temperature of 130 C. The yarn, whichshrank approximately 20% while passing through the slot, was thencollected on a rotating bobbin under the lowest tension commensuratewith good winding and unwinding performance. The bobbin package thusformed was then heated in an oven' (dry air) for a period of 1 hour at atemperature of C. The final yarn possessed a tenacity of 4.66 grams perdenier and an elongation of 20%, with loop and knot tenacities 01' 3.3and 2.3 grams per denier respectively. The yam was substantiallycolorless and showed no signs of having been degraded by the heattreatment.

, Earn: 11

A crystalline oriented acrylonitrile polymer yarn was formed byextruding a 20% solution of acrylonitrile polymer possessing an averagemolecular weight of appnoximately 120,000 in dimethyl formamide into aglycerol bath maintained at a temperature of 125 C., the yarn beingpassed through the bath for a distance of 24 inches and subjected to aspinning tension of approximately 1 gram per denier. The physicalproperties of this yarn, as spun, are given in the accompanying table.

One portion'or this yarn was wound into skeln form and suspended in atensionless, relaxed manner for a period of 1 hour in a glycerol bathheated to 100 C., whereupon the yarn shrank approximately 20% of itsoriginal length. A second portion or the yarn was heated for 1 hour inair at 100 C., the yarn being maintained at constant length during theheating period so that no shrinkage could take place. The physicalproperties of the yarn obtained in these manners are given in theaccompanying table, which clear- 1y indicates the nature of theimprovement obtained by the practice of this invention:

Table d Yum 'llamolflec (g p Elongation, per cent Straight Knot LoopStraight Knot Imp As spun a 15 1.1: 1. so 10.0 s. s a. 1 Heated 100 0.,1 hour. relaxed in yoerol 4.11 2.2 2. 75 21.0 14.0 18.0 Heated III)" 0.,1 hour, in llr0% 4.10 2.2 2.5 13.0 6.0 6.3

tures employed'in these operations should generally be of the order ofat least 80 C.; for example, desirable results are obtained with the useof a temperature of 100 C. to 150 C., and even higher temperatures, suchas up to and including 300 (Lean be used if desired. 1

For the relaxing step,- it is essential that the yarn be maintained in atenslonless manner so that it will be completely free to shrink. Asindicated in the examples, this step can be performed in a continuousmanner (on the run by leading the yarn in a relaxed manner through aheating'means) or in a batch manner (by suspending a quantity of yarn ina relaxed manner,

as in the form of a skein, in a heated medium).

- The exact manner of heating the yarn in this operation is not criticalto the invention, it only being necessary that the yarn be free toshrink during the heating operation; for example, the yarn may be heatedby passing through a slot formed in a heated block, as in Example I, orit can be passed about a heated roller, or it can be passed through aheated inert fluid, such as air,

glycerol, etc., the yarn being maintained in a relaxed, free-to-shrinkcondition.

The second step of the process of this invention, involving theprolonged heat treatment of the yarn, may also be conducted in either acontinuous or batch manner. However, because of the time involved, it isgenerally preferred to employ the latter procedure, wherein individualmasses of yarn, such as bobbin packages, are placed in a heating means,such as an oven, for the necessary length of time. The exact timerequired for the development of optimum physical properties in the yarnis, of course, dependent on the temperatures employed. Desirable resultsare obtained when using a heating period of 3 hours at 150 C. whilesomewhat longer periods should be used at a temperature of 80 C. Theheated medium employed for this operation comprises an atmosphere of airmaintained at the desired temperature. However, this is not essentialand in order to more substantially prevent discoloration the yarn ispreferably heated in any inert atmosphere, such as carbon dioxide ornitrogen gas, or even in an inert liquid, such as glycerine, glycol,etc.

The process of the invention preferably comprises the combined steps ofsuccessively subjecting an oriented acrylonitrile polymer yarn to a hotrelaxing treatment and to a prolonged heat treatment because of thedesirable effects of such treatment on both the tenacity. and elongationof the yarn. However, such a combined treatment is not essential for theproduction of an improved yarn, and desirable yarns for certain purposescan be obtained by the application of only the relaxing treatment or theheat treatment; for example, in the case of the yarn of Example I above,the omission of the final heating of the bobbin package yields a yarnpossessing a tenacity of 3.5 grams per denier and an ,6 s elongation of23%. On the other hand, as shown in Example II, the omission of therelaxing step results in the formation of a yarn that possesses agreatly improved tenacity but only a slightly improved elongation.

Though in the preferred form of the invention the two steps areperformed separately in different' apparatus, the two steps maybecombined and performed in a single apparatus. In such an embodiment,the yarn is placed'into a heated chamber and maintained therein at theappro priate temperature until the yarn has completely shrunk and theshrunken yarn has been'given I the prolonged heat treatment.

Although the specific examples of this case dis- I close onlyjthe'treatment of yarns prepared from a simple acrylonitrile polymer,the process of the invention is also applicable to the treatment: of

other shaped articles of sucha polymer, including films, tubings,fibers, B120.- The'acrylonitrile polymer constituting the shapedarticles treated in accordance with this invention must, of course, beof a-sumciently high molecular weight to pos sess filmorfilament-forming properties, and

polymers possessing an average molecular weight (determined fromviscosity measurements by the Staudinger formula) of from 7,000 to400,000'or more'are suitable for use. Preferablvhowever, the polymerpossesses a molecular weight of from 50,000 to 150,000. Though thepolymer preferably comprises a simple polymer of acrylonitrile, theinvention is not restricted thereto. Interpolymers of acrylonitrile andother polymerizable substances, such as vinyl compounds, unsaturatedcarboxylic acid and their derivatives, oleflnic' compoun'cL'and otherpolymerizable substances, may also be used. However, for the finalarticle to possess the desirable properties of polymerized acrylonitrile(such as resistance to acids and common solvents), it is necessary thatthe interpolymer contain a major portion of acrylonitrile, and thoseinterpolymers that are prepared from at least 80 parts of acrylonitrileand no more than 20 parts of another polymerizable substance arepreferred. As previously mentioned, it is, of course, necessary that thestructure to be treated possess an orientation as determined by X-rayanalysis; that is, at least equal to that of an unoriented acrylonitrilepolymer yarn that has subsequently been drawn to at least twice itsoriginal length. If the structure does not possess an orientation of atleast this value, the process of this invention will not generallyimprove its physical properties.

This invention makes possible the production or an acrylonitrile polymeryarn that is eminently suited for use in the textile art. The practiceof the invention not only greatly increases the elongation of such ayarn but also makes possible a substantial improvement in its tenacity.It also serves to greatly improve the knot and loop tenacities andelongations of the yarn. The invention makes possible for the first methe production of an acrylonitrile polymer yarn possessing a tenacity ofat least 4 grams per denier and an elongation of the'order of 20%. Atthe same time the yarn retains such other desirable properties,characteristic of acrylonitrile polymer yarn, as high resistance tochemical agents, such as common organic solvents, cleaning agents,etc.Moreover, the process of the invention does not cause the yarn to becomecolored to any appreciable extent. This fact, together with theirgreatly improved physical properties, makes the yarn of this inventionhighly suited for use in the textile art. Moreover, the yarns do nottend to shrink to any appreciable extent on subuquent exposure toelevated temperatures for example, shrinkage of the yarns underconditions Since it is obvious that many changes sntl modifications canbe made in the above-described details without departing from the natureand spirit of the invention, it is to be understood that the inventionis not to be limited thereto except as set forth in the appended claims.

I claim:

1. A method oi improving the physical properties of an oriented shapedarticle formed -1'rom a polymer containing a ajor proportion oracrylonitrile which comprises heating the shaped article 'in a relaxed,iree-to-shrink condition. at a temperature of 80C. to 300 C. andmaintaining the shrunken shaped article under a tension insuihcient to stretchsaid shrlmlr'en article at a temperature oi 80 C. to 300 C. for at leastone hour. both of said heating stepsbeing carriedvout in the presence ofan inert heating medium.

2. The'method of improving the physical properties oran oriented yarnformed. from: polymer containing a major proportion otacrylonitrilewhich comprises heating. the yarn in a relaxed, i'ree-to-shrinkcondition at a temperature of. 89 C. to 300 C. and maintainingtheshrunken yarn under a tension insumcient to stretch said shrunkenyarn at a temperature of 80 C. to 300 is P ., 8CJoratleastonehounbothoteaid heatingstepsbeing elected in the presenceof an inert heating medium.

3. Themethod of claim2,characterizedinthat said second heating stepiscarried out-in an inertatmosphere.

4. The method of claim 2, characterized in that said second heating stepis carried out while the yarn is maintained ulder a tension 01 not more10 than 0.05 gramper denier.

a tile of this patent:

Number 6 Name Date 1,367,297 Zart July 12, 1932 2,161,766 Rugeley et a1.(1) June 6, 1939 2,170,439 Wiezevich Aug. 22, 1939 2,176,153 Semon Oct.17, 1939 2,199,411 Lewis May 7, 1940 2,239,730 Fikentscher et al. Apr.29, 1941 2,273,071 Rugeley et al. (2) Feb. 17, 1942 2,309,370 WilliamsJan. 26, 1943 2,317,409 Seaton Apr. 27, 1943 2,325,060 Ingersoll July27,1943 2,346,203 Conaway Apr. 11, 1944 85 I V FOREIGN PATENTS NumberCountry Date 387,956 Great Britain Feb. 16, 1933

